4. It's not just about email
One of the biggest mistakes a company can make is to justify a move to Gmail and Docs on the basis that they're great individual productivity tools. In many organisations, such tools are only part of the everyday workflow: email systems tie in with special-purpose addons that link them with faxing, archiving, security or other systems. Documents are scanned and fed through scripted routines for parsing, OCR processing, and further actions. Messages and documents are backed up and archived automatically, on site.
In a Google world, all of this goes away immediately. Sure, Google offers a range of extensions that links its tools with other hosted environments – but if your company has a well-established workflow that keeps it operating, and it can't survive the withdrawal of Outlook or Office, you may want to reconsider your move. Business process change is tricky business, and you'll need to make sure you can deliver equivalent or better functionality before making the switch. Conduct an extensive process review and be prepared for a conclusion that says you should sit tight until cloud offerings get flexible enough to suit your requirements.
5. There are other ways
You may like the idea of having someone else look after the security and accessibility of your email and documents, but you're not limited to Google's options to make your life easier. Many organisations are finding life far simpler than ever by revisiting their Exchange hosting arrangements and allowing third-party providers to take over the task of running key business process servers.
Taking this approach will give you the benefits of hosting your email in a high-security, high-availability environment without having to buy into the Google way of doing things. You'll be able to keep your familiar interfaces, avoid dramatic changes to corporate workflow, and improve availability overall; if you're later keen on Google's offerings, you can slowly move users to them as the urge takes you.
If you decide to roll your own, of course, you'll also need to consider ways to match Google's features. In the main, this means ensuring that you have adequate mail and document scanning in place, and that you have provided some accommodation for user mobility. Google has extended its online platforms to mobile devices in a very smooth way, and you'll need to make sure you can do the same or you may find users will be taking their own steps to make it happen. In fact, they'll probably be adopting Google on their own anyway; no matter what your reasons why, if you decide not to take that step, be prepared to formalise a policy for dealing with those that do.